Trench transistor and method for fabricating a trench transistor

ABSTRACT

A trench transistor having a semiconductor body, in which a trench structure and an electrode structure embedded in the trench structure is disclosed. The electrode structure is electrically insulated from the semiconductor body by an insulation structure. The electrode structure has a gate electrode structure and a field electrode structure arranged below the gate electrode structure and electrically insulated from the latter. There is provided between the gate electrode structure and the field electrode structure a shielding structure for reducing the capacitive coupling between the gate electrode structure and the field electrode structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Divisional Patent Application claims priority to U.S. patentapplication Ser. No. 11/513,969, filed on Aug. 31, 2006, which claimspriority to German Patent Application No. DE 10 2005 041 256.4, filed onAug. 31, 2005, both of which are incorporated herein by reference.

BACKGROUND

One aspect of the invention relates to a trench transistor and to amethod for fabricating a trench transistor.

Trench transistors have a semiconductor body, in which a trenchstructure and an electrode structure embedded in the trench structureare provided. The electrode structure is electrically insulated from thesemiconductor body by means of an insulation structure. In the case of afield plate trench transistor, the electrode structure is divided into agate electrode structure and a field electrode structure arranged belowthe gate electrode structure, in which case the field electrodestructure may be electrically insulated from the gate electrodestructure.

It is always an aim to further increase the integration density of thetrench transistors. This may be effected, on the one hand, by reducingthe distances between the individual trenches of the trench structure(that is to say that the width of that part of the semiconductor bodywhich is situated between the trenches (“mesa zones”) is reduced). Onthe other hand, the width of the trenches themselves may be reduced. Ifuse is made of the second possibility, that is to say that the width ofthe trenches is reduced, then it is generally necessary likewise toreduce the thickness of the insulation structure which electricallyinsulates the field electrode structure from the semiconductor body(since the reduction of the insulation structure thickness has a great“miniaturization potential”). This is problematic, however, since, inthe case of excessively thin insulation layers between the fieldelectrode structure and the semiconductor body, particularly in the caseof fast switching operations, strong capacitive coupling effects occurbetween the drain/drift region of the trench transistor and the gateelectrode structure (coupling of drain/drift region—field electrodestructure—gate electrode structure) if the field electrode structure iselectrically insulated from the gate electrode structure.

SUMMARY

One aspect of the invention specifies a trench transistor which has anincreased degree of miniaturization compared with the prior art, but atthe same time avoids such coupling effects.

The trench transistor according to one embodiment of the invention has asemiconductor body, in which a trench structure and an electrodestructure embedded in the trench structure are provided. The electrodestructure is electrically insulated from the semiconductor body by aninsulation structure. The electrode structure has a gate electrodestructure and a field electrode structure arranged below the gateelectrode structure and electrically insulated from the latter. There isprovided between the gate electrode structure and the field electrodestructure a shielding structure for reducing the capacitive couplingbetween the gate electrode structure and the field electrode structure.The shielding structure accordingly serves for reducing electromagneticor electrostatic coupling effects between the gate electrode structureand the field electrode structure.

The use of a shielding structure has the effect that even in the case ofa high degree of integration, that is to say in the case of a smalltrench width, coupling effects between the gate electrode structure andthe field electrode structure can be kept small.

The shielding structure may be configured in a wide variety of ways. Byway of example, it is possible to configure the shielding structure as ashielding electrode which is at a fixed potential and which iselectrically insulated from the gate electrode structure, the fieldelectrode structure and the semiconductor body. The shielding electrodeis preferably at source potential, but may also be at any otherpotential.

If the shielding structure is realized as a shielding electrode, thenthe sum of the internal resistances of the shielding electrode and thecurrent/voltage supply of the shielding electrode should be less thancorresponding internal resistance sums for the gate electrode structureand the field electrode structure. This has the advantage that theshielding electrode scarcely couples to rapidly changing drainpotentials or space charge zone potentials, whereby a good shieldingeffect is ensured.

The shielding structure may also be realized by a shielding insulationlayer, the thickness of which is greater than the thickness of theinsulation structure region which insulates the field electrodestructure from the semiconductor body. As an alternative, the thicknessof the shielding insulation layer may turn out to be greater than doublethe thickness of the insulation structure region which insulates thegate electrode structure from the semiconductor body, or may turn out tobe greater than double the thickness of the insulation structure regionwhich insulates the field electrode structure from the semiconductorbody.

The shielding insulation layer may be formed as a layer sequence havinga first oxide layer, a nitride layer and a second oxide layer.

If the shielding structure is realized in the form of a shieldinginsulation layer, then, in one embodiment, the k value of the shieldinginsulation layer is less than the k value of the insulation structure.By means of the low k value it is possible, in a manner similar to thatin the case of the shielding electrode, to achieve a significantreduction of the capacitive coupling between the gate electrodestructure and the field electrode structure.

In a further embodiment, the shielding structure is realized in the formof a cavity.

The horizontal distances between the shielding structure and thesemiconductor body may, in order to improve the shielding effect, turnout to be less than the horizontal distances between the gate electrodestructure and the semiconductor body.

One aspect of the invention furthermore provides a method for producingthe trench transistor described above. The method proceeds from apreprocessed semiconductor body, in which a trench structure and a fieldelectrode structure embedded in the trench structure are provided, thefield electrode structure being electrically insulated from thesemiconductor body by a field electrode insulation structure. The methodis characterized by the following processes: firstly, insulatingmaterial is deposited on the field electrode structure. A gate electrodeinsulation structure is then formed. Finally, a gate electrode structureis formed.

The method according to one embodiment of the invention is suitable forthe fabrication of a trench transistor whose shielding structure isrealized in the form of a shielding insulation layer. The methodaccording to the invention makes it possible to set the thickness of thedeposited insulating material as desired, whereby the intensity of theshielding effect can likewise be set as desired.

The process of depositing insulating material preferably includes thefollowing process of: forming a protective oxide layer on thesemiconductor body, forming a silicon nitride or polysilicon layer onthe protective oxide layer, filling the remaining free spaces in thetrench structure with insulating material, and etching back theresulting layer composite having protective oxide layer, silicon nitrideor polysilicon layer and the insulating material into the trenchstructure as far as a specific depth, so that the insulating materialhas a desired thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 illustrates a detail from a conventional trench transistor incross-sectional illustration.

FIG. 2 illustrates a detail from a conventional trench transistor incross-sectional illustration.

FIG. 3 illustrates a detail from a conventional trench transistor incross-sectional illustration.

FIG. 4 illustrates an enlarged detail from the trench transistorillustrated in FIG. 3, in cross-sectional illustration.

FIG. 5 illustrates a detail from a first embodiment of the trenchtransistor according to the invention, in cross-sectional illustration.

FIG. 6 illustrates a detail from a second embodiment of the trenchtransistor according to the invention, in cross-sectional illustration.

FIG. 7 illustrates a detail from a first embodiment of the trenchtransistor according to the invention, in cross-sectional illustration.

FIGS. 8A to 8J illustrate a first to tenth process of a embodiment ofthe fabrication method according to the invention.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

In the figures, identical or mutually corresponding regions, componentsor component groups are identified by the same reference numerals.Furthermore, the doping types of all embodiments may be configuredinversely, that is to say that n-type zones can be replaced by p-typezones, and vice versa.

FIG. 1 illustrates a detail from a trench transistor 1 having asemiconductor body 2, in which a trench structure 3 is formed (only onetrench of the trench structure 3 can be seen in FIG. 1). An electrodestructure is provided in the trench structure 3, said electrodestructure being electrically insulated from the semiconductor body 2 byan insulation structure 5. Electric currents running vertically in thesemiconductor body 2 can be generated and controlled by means of theelectrode structure 4. The entire electrode structure 4 is at gatepotential. This has the disadvantage that a high gate-drain capacitanceoccurs between the electrode structure 4 and the drift zone/drain zonesituated below the trench structure 3 and alongside the trench structure3, which leads to high switching losses.

In order to combat this problem, it is known, as is illustrated in FIG.2, to divide the electrode structure 4 into a gate electrode structurepart 4 ₁ and a field electrode structure part 4 ₂. In this case, thefield electrode structure part 4 ₂ is at source potential and the gateelectrode structure part 4 ₁ is at gate potential. This division makesit possible to bring about a noticeable reduction of the gate-draincapacitance.

If, as is illustrated in FIG. 3, the width of the trenches of the trenchstructure 3 is to be reduced, the thickness of the insulation structure5 has to be greatly reduced. The consequence of this, however, is thatthere is a high capacitive coupling between the field electrodestructure part 4 ₂ and the drain zone/drift zone present below/alongsidethe trench structure 3 in the semiconductor body 2. Fluctuations in thedrain potential are thus transferred to a very great extent to thepotential of the field electrode structure part 4 ₂. The resultingpotential fluctuations in the field electrode structure part 4 ₂ are inturn transferred to a great extent to the potential prevailing at thegate electrode structure part 4 ₁, which is undesirable.

FIG. 4 reveals a more detailed version of the trench transistor 30illustrated in FIG. 3. The trench transistor 30 has a drain contact (forexample metal contact) 6, on which a semiconductor body 2 is provided. Adrain zone 7, a drift zone 8 and a body zone 9 are formed within thesemiconductor body 2. A trench structure 3 is provided in thesemiconductor body 2, a gate electrode structure part 4 ₁ and a fieldelectrode structure part 4 ₂ being embedded in said trench structure.The gate electrode structure part 4 ₁ and the field electrode structurepart 4 ₂ are electrically insulated from the semiconductor body 2 by aninsulation structure 5 (which is configured in thickened fashion in thelower region of the trench structure 3 (field oxide) and is configuredin thinned fashion in the upper region (gate oxide)). Source zones 10are formed in the body zone 9. The source zones 10 and the body zone 9are contact-connected by means of a source contact 11, the gateelectrode structure part 4 ₁ being electrically insulated from thesource contact 11 by an insulation structure 12.

FIG. 5 illustrates a first embodiment 40 of the trench transistoraccording to the invention. This embodiment differs from the embodimentillustrated in FIG. 3 and in FIG. 4 merely by the fact that a shieldingelectrode 13 at a fixed potential (here: source potential) is providedbetween the gate electrode structure part 4 ₁ and the field electrodestructure part 4 ₂. A more detailed representation of the embodiment 40can be seen in FIG. 6. The potential of the field electrode structurepart 4 ₂ may be at a fixed value or be a floating potential.Furthermore, it is possible to put different parts of the fieldelectrode structure part 4 ₂ (designated here by H1, H2 and H3) atrespectively different potentials. The potential of the shieldingelectrode 13 is preferably at source potential and the potential of thegate electrode structure part 4 ₁ is at gate potential. In oneembodiment, the sum of the internal resistances of the shieldingelectrode 13 and the current/voltage supply of the shielding electrode13 is less than corresponding internal resistance sums for the gateelectrode structure part 4 ₁ and the field electrode structure part 4 ₂.

FIG. 7 illustrates a further embodiment 50 of the trench transistoraccording to the invention. This embodiment differs from the embodiment40 illustrated in FIG. 6 merely by the fact that the shielding electrode13 is replaced by a cavity 14 adjoined by the upper end of the fieldelectrode structure part 4 ₂ and the lower end of the gate electrodestructure part 4 ₁. As an alternative, the shielding electrode 13 isreplaced by an insulation layer 15 having a low k value and/or a largevertical extent. Each of the alternatives mentioned makes it possible toreduce the coupling between the gate electrode structure part 4 ₁ andthe field electrode structure part 4 ₂.

The description below describes, with reference to FIGS. 8A to 8J, amethod for fabricating the insulation layer 15 or a method forfabricating a trench transistor containing an insulation layer of thistype. In all of the figures, the left-hand part illustrates across-sectional illustration and the right-hand part illustrates alongitudinal section illustration corresponding thereto.

In a first process, a trench structure 3 is introduced into asemiconductor body 2, for example by means of an etching process (FIG.8A). In a second process (FIG. 8B), a field electrode insulationstructure 5 ₂ (field plate oxide) is produced on the surface of thesemiconductor body 2, for example by means of a thermal oxidationprocess. In a third process (FIG. 8C), polysilicon is introduced intothe trench structure 3 in order to produce a field electrode structure 4₂. In a fourth process (FIG. 8D), the field electrode insulationstructure 4 ₂ is etched back into the trench in such a way that theupper ends of the remaining field electrode insulation structure 5 ₂ liebelow the vertical position of the upper end of the field electrodestructure 4 ₂. In a fifth process (FIG. 8E), a first insulation layer 16is applied on the surface of the resulting layer composite. In a sixthprocess (FIG. 8F), a silicon nitride or polysilicon layer 17 isdeposited onto the first auxiliary insulation layer 16. In a seventhprocess (FIG. 8G), remaining free spaces within the trench structure 3are filled with TEOS (tetraethyl orthosilicate (deposition oxide)) 18.In an eighth process (FIG. 8H), part of the TEOS material is removed(for example by means of an etching process) in such a way that aresidue of the TEOS material 8 remains only within the trench structure3. In a ninth process (FIG. 8I), the silicon nitride/polysilicon nitridelayer 17 and the auxiliary insulation layer 16 are partly removed (abovea vertical position corresponding to the vertical position of the topside of the TEOS layer 18). In further process (indicated by FIG. 8J), agate electrode insulation structure is produced above the layercomposite including the auxiliary insulation layer 16, the siliconnitride/polysilicon layer 17 and the TEOS layer 18, and a gate electrodestructure is subsequently formed (not illustrated here). Further processrequired through to the completion of the trench transistor are known tothe person skilled in the art.

Further aspects of the invention will be explained in the descriptionbelow.

In the development of new generations of DMOS power transistors, oneimportant aim is to reduce the on resistivity R_(on)·A. In order toachieve this, attempts are made in known trench transistor concepts toreduce the pitch further. This may be effected, on the one hand, byreducing the mesa width between the trenches (dense trench concepts),but on the other hand the trench width itself may be reduced. For highervoltage classes (>40 V), in particular, a reduction of the field oxidethickness is appropriate in the field plate trench concept. The way inwhich this is achieved without disturbing influences (feedbacks) on thedevice parameters (switching speeds) is the subject matter of thisinvention.

One known method for reducing the on resistivity consists in departingfrom the planar cell structure and using trench cells. As a result, thechannel resistance, in particular, is reduced by a significant increasein the channel width per area. The resistance of the drift path(epitaxial resistance) can be reduced by using deep trenches (documentU.S. Pat. No. 4,941,026). A field plate trench concept with a gateelectrode in the trench is proposed in that case (FIG. 1), but onaccount of its relatively large overlap with the epitaxial layer andthus the drain zone, said gate electrode has very high gate-draincapacitances, which in turn lead to high switching losses. Therefore, inrecent trench transistor generations, besides a gate electrode in theupper trench region, a source electrode in the trench bottom region(FIG. 2) is also used for reducing the gate-drain capacitances (documentU.S. Pat. No. 5,998,833). If, on the other hand, the field plate conceptis intended to be applied for higher voltage classes of >40 V totypically a few hundred volts, then it is necessary as far as possibleto reduce primarily the field oxide thickness (“fox”) in the trenchbottom region in order both to achieve a lower on resistance by means ofthe smaller pitch and to ensure the technological feasibility of a thickoxide in the trench bottom. This can be achieved by introducing one or aplurality of auxiliary electrodes (H3) in the trench bottom region, theauxiliary electrodes being put at a suitable varying potential or beingat floating potential (DE 103 39 455.9, also see FIG. 3). Onedisadvantage in this case arises, however, from the fact that such anauxiliary electrode or the voltage supply for such an auxiliaryelectrode (particularly if it is realized on the chip) has a relativelyhigh internal resistance (Ri) and this results, in the event of rapidswitching, in feedback effects of the drain potential via H3 to the gateelectrode situated directly above the latter. Ri_(H3) shall hereinafterbe the sum of the internal resistances of H3 and the voltage sourcedriving H3. If H3 is floating, then this corresponds to an Ri havinginfinite magnitude.

In order to avoid/reduce feedback effects to the gate electrodes offield plate transistors, according to the invention a (locally small)source electrode is introduced between the gate electrode in the uppertrench region and the auxiliary electrodes in the trench bottom regionfor shielding purposes. This is illustrated in FIG. 5. For the sake ofsimpler illustration, here it is the case that there is only ever oneauxiliary electrode (H3) illustrated in the trench bottom region.However, it is also possible for a plurality of auxiliary electrodes tobe provided, as is illustrated in FIG. 6 (H3, H4, H5 . . . ).

Generally, the gate electrode has a relatively low Ri_(gate), so that,in the case of a rapidly changing drain potential, hardly any positivefeedback effects to the gate electrode arise. If, in order to reduce thefield oxide thickness in the trench bottom region, use is made of one ora plurality of auxiliary electrodes H3, H4, having very high Ri onaccount of the small cross section, the low doping or the fact that theyare connected via long leads (Ri_(H3) of the auxiliaryelectrode>>Ri_(gate) of the gate electrode) or owing to the highinternal resistance of the voltage source, in the case of the rapidlychanging drain potential, this results in strong positive feedbackeffects to the auxiliary electrodes and, by virtue of the directproximity of the auxiliary electrodes to the gate electrode, indirectlyalso to the gate electrode. In the extreme case where the auxiliaryelectrode is floating, Ri_(H3) is infinite and the auxiliary electrodesfollow the drain potential or the potential in the adjacent space chargezone almost simultaneously. As a result, the gate potential is alsochanged in an undesirable manner.

According to the invention, an additional source electrode is introducedinto the region between auxiliary electrode and gate electrode and itthen shields the influence of the potentials established in theauxiliary electrodes on the gate electrode. On account of its very lowRi, said source electrode scarcely couples to a rapidly changing drainpotential or a potential in the space charge zone and is thus highlysuitable for shielding. Furthermore, a particularly thick field oxide isnot required in the region of the introduced source electrode since onlya fraction of the maximum drain voltage in the off-state case is presentthere (typically approximately 10% of the reverse voltage).

The invention accordingly introduces a local small source electrode intothe region between the gate electrode and one/a plurality of auxiliaryelectrodes in the trench of a field plate trench transistor for thepurpose of shielding from feedback effects.

The shielding electrode at source potential can be used in all trenchtransistors, in particular in field plate trench transistors (and inthis case once again particularly in transistors having one or aplurality of auxiliary electrodes in the trench), the field plates(field electrodes) of which are at a potential U1 between sourcepotential and drain potential or are configured in floating fashion. Thewidth of the shielding electrode is intended essentially to correspondto the width of the gate electrode (very good shielding). The oxidelayers between source shielding electrode and adjacent epitaxial layermay turn out to be thin and may even be in the region of the gate oxidethickness since typically only a fraction of the drain voltage isdropped across this region.

In the development of new generations of DMOS power transistors,reducing the gate-to-drain capacitance is of great importance in orderto be able to effect faster switching or to be able to use lower-powerdrivers. In order to achieve a low gate-to-drain capacitance, theintention is to use, in addition to a field electrode at variablepotential, a gate electrode that is decoupled as well as possible fromthe variable field electrode. The field electrode permits a reduction ofthe field oxide, particularly in the case of higher voltage classes.Instead of one field electrode, it is also possible to use a pluralityof field electrodes which lie one above another and which are atdifferent potentials.

What is disadvantageous about known field plate trench transistors isthat the thickness of the dielectric which isolates the gate electrodefrom the field electrode (field plate) is generally coupled with thethickness of the gate oxide on account of the process sequence.Furthermore, on account of the complicated diffusion conditions, weakpoints or thinned portions may form in said dielectric, which greatlyrestrict the reliability of the DMOS components.

The invention accordingly provides a structure which realizes a fieldplate, a gate oxide, a field electrode, a dielectric (or anoxide-metal-oxide sandwich) and a gate electrode with little spacerequirement in a trench. In this case, the dielectric (or anoxide-metal-oxide sandwich) is realized independently of the gate oxideprocess, so that its thickness can be set freely and the gate-to-draincapacitance can thus also be reduced. The advantages are a lowergate-to-drain capacitance and an increased reliability.

Therefore, one aspect of the invention consists in making the capacitivecoupling between gate electrode and field electrode as small aspossible. This can be achieved by increasing the distance between gateelectrode and field electrode and/or reducing the relative permittivityof the insulating material between gate electrode and field electrode.The insulating material should be designed as a low-k material, that isto say as a material which preferably has a lower relative permittivitythan oxide.

In order to fabricate the insulating material between the gate electrodeand the field electrode, it is possible, after the etching of the fieldplate oxide with the aid of the variable field plate (polysilicon), toprotect the channel region of the transistor by means of two layers (anoxide and a polysilicon or nitride). An oxide is then deposited andetched back again. A dielectric thus arises from the three layers, whichdielectric isolates the variable field electrode from the gateelectrode, and its thickness can be largely freely configured. The aimof reducing the gate-to-drain capacitance is thus achieved. After theetching back, the two auxiliary layers applied first are removed again.The process is subsequently continued in a known manner (gate oxidationand production of the gate poly).

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

1. A method for producing a trench transistor from a preprocessedsemiconductor body, comprising: providing a trench structure; providinga field electrode structure embedded in the trench structure; whereinthe field electrode structure is electrically insulated from thesemiconductor body by a field electrode insulation structure by:depositing insulating material on the field electrode structure; forminga gate electrode insulation structure; forming a gate electrodestructure; and providing a shielding electrode at a fixed potential andelectrically insulated from the gate electrode structure, the fieldelectrode structure and the semiconductor body.
 2. The method of claim1, wherein the deposition of insulating material comprises: forming aprotective oxide layer on the semiconductor body; forming a siliconnitride or polysilicon layer on the protective oxide layer; filling theremaining free spaces in the trench structure with insulating material;and etching back the resulting layer composite comprising protectiveoxide layer, silicon nitride or polysilicon layer and the insulatingmaterial into the trench structure as far as a specific depth, so thatthe insulating material has a desired thickness.
 3. The trench method ofclaim 1, wherein the shielding electrode is at source potential.
 4. Themethod of claim 1 further comprising configuring the internalresistances of the shielding electrode and the current/voltage supply ofthe shielding electrode such that their sum is less than a correspondinginternal resistance sums for the gate electrode structure and the fieldelectrode structure.
 5. The method of claim 1 further comprising forminga shielding structure with a shielding insulation layer, the thicknessof which is greater than the thickness of the insulation structureregion which insulates the field electrode structure from thesemiconductor body.
 6. A trench transistor, having a semiconductor body,comprising: a trench structure; an electrode structure embedded in thetrench structure; the electrode structure being electrically insulatedfrom the semiconductor body by an insulation structure and having a gateelectrode structure and a field electrode structure arranged below thegate electrode structure and electrically insulated from the latter; andthere being provided between the gate electrode structure and the fieldelectrode structure a shielding structure for reducing the capacitivecoupling between the gate electrode structure and the field electrodestructure, wherein the shielding structure has a shielding insulationlayer, the k value of which is less than the k value of the insulationstructure; and a shielding electrode at a fixed potential andelectrically insulated from the gate electrode structure, the fieldelectrode structure and the semiconductor body.
 7. The trench transistorof claim 6, wherein the shielding electrode is at source potential. 8.The trench transistor of claim 6, wherein the sum of the internalresistances of the shielding electrode and the current/voltage supply ofthe shielding electrode is less than corresponding internal resistancesums for the gate electrode structure and the field electrode structure.9. The trench transistor of claim 6, wherein the thickness of theshielding insulation layer is greater than double the thickness of theinsulation structure region which insulates the gate electrode structurefrom the semiconductor body, or greater than double the thickness of theinsulation structure region which insulates the field electrodestructure from the semiconductor body.
 10. The trench transistor asclaimed in claim 9, wherein the shielding insulation layer is a layersequence comprising a first oxide layer, a nitride layer and a secondoxide layer.
 11. The trench transistor as claimed in claim 6, whereinthe shielding structure is a cavity.
 12. The trench transistor asclaimed in claim 6, wherein the horizontal distances between theshielding structure and the semiconductor body are less than thehorizontal distances between the gate electrode structure and thesemiconductor body.
 13. A method for producing a trench transistorcomprising: providing a trench structure; forming a field electrodestructure embedded in the trench structure; depositing insulatingmaterial on the field electrode structure; forming a gate electrodeinsulation structure; forming a gate electrode structure; wherein thefield electrode structure is electrically insulated from a semiconductorbody by a field electrode insulation; and forming a shielding electrodeat a fixed potential and electrically insulated from the gate electrodestructure, the field electrode structure and the semiconductor body.